Many night vision systems use image intensifiers as optical amplifiers. The image intensifier may generally comprise a photocathode to convert input photons into electrons, a microchannel plate (MCP) to multiply the electrons and a phosphor screen to convert the electrons back to photons, thus displaying an intensified image. The photoelectrons accelerate under the influence of an applied electrical field from a power supply and reach the MCP. An electrical field is also applied to the MCP where a secondary electron emission occurs which may multiple the number of electrons by several orders of magnitude.
When using a conventional image intensifier, the image is intensified as a whole, namely all the pixels are intensified by the same amount. The amount of the amplification is related to the number of electrons that pass to the MCP and may be controlled by changing the potential gradient across the device. In conventional image intensifiers, however, it may not be possible to control selectively only certain electrons that are associated with a specific segment of an input image. Consequently, in some environmental conditions, the quality of the intensified image may be poor. For example, an intense source of light, such as, for example, a street lamp, that passes into the field of view may mask the image of a darker area in its vicinity.
Furthermore, conventional image intensifiers may not enable certain desirable applications, such as, for example, to plant an external image on part of the field of view of an intensified image without loss of high quality performance. This exemplary application is particularly useful in devices, such as, night vision goggles (NVG), typically used by pilots.
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